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Influence of microplastic-associated biofilms on the bioavailability of a mixture of cadmium and benzo[a]pyrene by the analysis of biomarker gene expression in larval zebrafish
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Researchers found that microbial biofilms — thin layers of bacteria that coat microplastics in water — selectively reduce how much of a toxic chemical called benzo[a]pyrene gets absorbed by larval zebrafish, while not affecting cadmium absorption, showing that microplastics can act as complex, biology-influenced carriers of multiple pollutants simultaneously.
Microplastics (MPs, 1 µm – 5 mm) in aquatic environments undergo complex weathering transformations such as those induced by microbial colonization and biofilm formation, that affect their ability to interact with environmental contaminants (co-contaminants). In this study, the microbial composition of MP biofilms and its influence on the sorption and bioavailability of two co-contaminants with different physicochemistry, benzo[a]pyrene (B[a]P) and cadmium (Cd) in a mixture, were assessed. Aqueous-phase bioavailability was measured by assessment of biomarker gene expression for these toxicants (cytochrome P450 1A, cyp1a, and metallothionein 2, mt2, for B[a]P and Cd respectively) in larval zebrafish, Danio rerio. Significant induction of cyp1a and mt2 gene expression (p < 0.05) was observed after exposure to the mixture of Cd, B[a]P and MPs compared to joint exposure with individual contaminants and MPs. Significant changes in bioavailability for mt2 biomarker (p < 0.001) resulted after exposure to a Cd and B[a]P mixture with MPs compared to the same exposure without MPs. Biofilms significantly reduced bioavailability of B[a]P (cyp1a gene expression (p < 0.01)) but not Cd (mt2 gene expression) in the mixture with Cd and B[a]P (HDPE + BF + B[a]P + Cd) compared to the same treatment without biofilm (HDPE + B[a]P + Cd). Thus, compared to Cd, the biofilm could provide additional interactions with B[a]P, and new specific active sites on the MPs surface, that reduced B[a]P bioavailability. Additionally, the biofilm microbial community included hydrocarbon-degrading bacteria able to metabolize hydrophobic chemicals. These data indicated that in a mixture of co-contaminants, the biofilm selectively influenced their bioavailability and that the microbial composition of MPs biofilm may have played a key role in reducing B[a]P bioavailability. The results of this study highlight how in a complex exposure scenario characterized by a mixture of different co-contaminants, the polymer and chemical properties and micro-surroundings of the organisms may affect contaminants' bioavailability and/or exposure.
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Researchers examined whether contaminants sorbed to microplastics become bioavailable when ingested by larval zebrafish, using phenanthrene and ethinylestradiol as test chemicals. The study found that microplastics can alter the bioavailability of co-contaminants, as evidenced by changes in biomarker gene expression in the fish larvae.
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Researchers exposed zebrafish to polystyrene microplastics combined with cadmium for three weeks and found that the presence of microplastics significantly increased cadmium accumulation in the liver, gut, and gills. The combined exposure caused greater oxidative damage, tissue inflammation, and disruption of protective gene activity than either pollutant alone. The study demonstrates that microplastics can enhance the toxicity of heavy metals in fish by acting as carriers that increase the body's uptake of harmful substances.
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Researchers investigated how polyethylene microplastics interact with the industrial chemicals bisphenol A and bisphenol AF in zebrafish, finding that microplastics can either reduce or worsen the toxicity depending on the specific chemical and biological pathway involved. For bisphenol A, the microplastics partially absorbed the chemical and reduced its harmful effects, but for bisphenol AF, they worsened toxicity to certain organ systems. The study reveals that microplastics play a complicated dual role in modifying how other pollutants affect aquatic life.
Determination of Bisphenol Compounds and the Bioaccumulation after Co-Exposure with Polyethylene Microplastics in Zebrafish
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Researchers developed a method to measure how bisphenol A and bisphenol S accumulate in zebrafish tissues when microplastics are also present. They found that microplastics increased the accumulation of these hormone-disrupting chemicals in fish tissues, with BPA building up more than BPS. The evidence indicates that microplastics can act as carriers that enhance the uptake of harmful chemicals by aquatic organisms.
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